Devices of this type are known in which a control stick is supported in a universal joint and, below the universal joint, by its extension engages into slots, located one above the other, of two crossed yokes which are supported swingably on extended shafts of the universal joint of the control lever. Outside the yokes these extended shafts form setting shafts of rotary rheostats. Depending on the position of the control stick, corresponding electric values are set in the rheostats. Such devices are used for instance for radio remote control of model aeroplanes as well as other models, but also they are used for controlling electrically operated wheelchairs and for other machines in which a plurality of values are controlled simultaneously and variably in proportion to each other.
In known devices of this type, rotary rheostats are turned with respect to their axes within given ranges by means of a special operating lever in order for instance to set a constant electrical value. In this way, in the case of a remote controlled model aeroplane, a control element can be set with a given deflection in order to achieve desired trim.
Such devices also are already known in which the control stick acts as a so called "open stick" on two crossed pivot shafts, also with use of and guidance in slots of crossed yokes which are seated on the pivot shafts, the pivot shafts being the axes of rotation of rotary rheostats which are arranged in fixed position in the frame. These rheostats can also be set in fixed position by a swing lever in order to give established values of trim.
In these known devices in which only a relatively small range effectively can be utilized in the rheostats (because of swinging motions of their shafts) these rheostats are of relatively small diameter. In the rheostats, wound resistance wires are tapped off by wiper contacts. These resistance wires must be of sufficient thickness, if only because of mechanical stress. Due to relatively short path of the wiper contact, upon a swinging motion in the rheostats of small diameter there thus results a relatively coarse stepwise progression from the transfer from one wire winding to the other and correspondingly large steps between the individual resistors which are tapped off by the wiper contact. In addition, the electrical values must in this connection be transmitted over two wiper points, namely on the one hand from the resistor to the wiper contact and on the other hand via a wiper ring to the wiper contact. The exact transmission of the roughly produced electrical values thereby becomes problematical and is subject to many disturbances, for instance as a result of dirt.
In the two known embodiments of these devices transfer of mechanical movements of deflection of the control stick over a large number of support points and slot guides, the bearing plays of which are cumulative, and thus due to mechanical conditions, by themselves prevent a given, relatively coarse accuracy in setting from being improved. This accuracy in adjustment also is affected negatively by relatively long transmission paths of mechanical forces, for instance in the slotted yokes, which (consisting of metal) are subjected, for the duration of their use and also under the influence of temperature variations, to deformations which are in part elastic and in part permanent.
Practically all known devices of this type are provided with a zero reset device for the control stick which device causes the control stick to have its position of rest in its central position. This zero return device acts via springs and stops and also is affected in its accuracy by cumulative bearing plays of different mechanical transmission members for movements of the control stick. In the known devices of this type, therefore, the central position of rest of the control stick is surrounded by a region of deflection in which no changes in the electric values are as yet produced.